1. Field of the Invention
The present invention relates to a voltage detection circuit for checking whether an input voltage is equal to a predetermined level or not.
2. Description of the Prior Art
FIG. 4 shows an example of the configuration of a conventional voltage detection circuit. In the voltage detection circuit shown in FIG. 4, when the voltage Vcc applied to an input terminal 5 is higher than a predetermined level Vsh, the voltage outputted from a terminal 4 is equal to the voltage Vcc; when the voltage Vcc applied to the input terminal 5 is lower than the predetermined level Vsh, the voltage outputted from the terminal 4 is equal to zero. Moreover, in the voltage detection circuit shown in FIG. 4, the voltage division factor of the voltage division circuit composed of resistors r1 to r3 and a diode-connected transistor Tr1, the base-emitter voltage of a transistor Tr4, the base-emitter voltage of a transistor Tr5, the resistance of a resistor r4, and the resistance of a resistor r5 are so set that the temperature coefficient of the predetermined level Vsh is equal to zero. Incidentally, the voltage detection circuit shown in FIG. 4 is disclosed in Japanese Patent Registered No. 3218641.
As described above, in the voltage detection circuit shown in FIG. 4, the voltage division factor of the voltage division circuit composed of the resistors r1 to r3 and the diode-connected transistor Tr1, the base-emitter voltage of the transistor Tr4, the base-emitter voltage of the transistor Tr5, the resistance of the resistor r4, and the resistance of the resistor r5 are so set that the temperature coefficient of the predetermined level Vsh is equal to zero. This means that the voltage detection circuit shown in FIG. 4 is absolutely required to be provided with the resistors r1 to r3, the transistor Tr1, the transistor Tr4, the transistor Tr5, the resistor r4, and the resistor r5.
As a result, the voltage detection circuit shown in FIG. 4, in which the temperature coefficient of the predetermined level Vsh used as the reference level for voltage detection can be made equal to zero, requires a larger number of circuit elements than a voltage detection circuit in which the reference level for voltage detection varies with temperature. Since an increase in the number of circuit elements constituting a circuit hampers its cost reduction and miniaturization, it is desirable to minimize such an increase in the number of circuit elements used. However, the voltage detection circuit shown in FIG. 4 is not composed of the minimum needed number of circuit elements.